The implant mimicked a process where cells broken loose from a tumour were attracted to other areas in the body by immune cells, the researchers said.

They found that these immune cells set up camp on the implant - a natural reaction to any foreign body - drawing the cancer cells in.

Initially, the researchers "labelled" cancer cells so they would light up and be easily spotted.

But they then moved on to a special imaging technique that can distinguish between cancerous and normal cells, and found they could detect cancer cells that had been caught in the implant.

Reduce spread

Unexpectedly, when they measured cancer cells that had spread in mice with and without the implant, they found that the device not only captured cancer cells, it reduced the numbers present at other sites.

Researchers have long been looking for ways to detect the spread - or metastasis - of cancer at an early stage, but cancer cells that circulate in the bloodstream are rare and hard to detect.

Study leader Prof Lonnie Shea, from the Department of Biomedical Engineering at the University of Michigan, said they were planning the first clinical trials in humans fairly soon.

"We need to see if metastatic cells will show up in the implant in humans like they did in the mice, and also if it's a safe procedure and that we can use the same imaging to detect cancer cells," he said.

He said they were continuing work in animals to see what happened to the overall outcome if cancer spread was detected at a very early stage - something which was not yet fully understood.